Void Filling Joint Prosthesis And Associated Instruments

ABSTRACT

A distal femoral joint replacement system includes a femoral component having condylar articular surfaces, a stem extending from the femoral component, and a void filler for filling a bone void within a femur. The void filler includes a body and a plurality of legs extending from the body. The body has a sidewall defining an opening for receipt of the stem which extends along a length of the body and extends through the sidewall so as to form a side-slot in the sidewall that extends along an entire length of the sidewall. The plurality of legs each have a first end connected to the body and a second end remote from the body. The legs each have an outer surface that tapers between the first and second ends and is configured to register with a corresponding inner surface of a bone void when implanted in an end of the femur.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/694,113, filed Nov. 25, 2019, which is a continuation of U.S.application Ser. No. 15/585,824, filed May 3, 2017, now U.S. Pat. No.10,524,806, which is a continuation of U.S. application Ser. No.14/208,718, filed Mar. 13, 2014, now U.S. Pat. No. 9,668,758, whichclaims the benefit of the filing date of U.S. Provisional PatentApplication No. 61/779,302, filed Mar. 13, 2013, the disclosures ofwhich are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Joint replacement surgery is a common orthopedic procedure for jointssuch as the shoulder, hip, knee, ankle and wrist. Prior to implantingprosthetic components in a joint of a patient, a surgeon generally hasto resect at least a portion of the patient's native bone in order tocreate a surface and/or recess or void for supporting, accepting orreceiving at least a portion of the prosthetic components beingimplanted. Generally, a surgeon only resects the amount of bone that isneeded in order to properly implant the prosthetic components in thejoint because once native bone is resected from a joint, it is goneforever. Thus, the surgeon typically attempts to maintain as much of thenative structural integrity of the joint as he or she can during theresection process.

When previously implanted prosthetic components fail for any one of avariety of reasons, a revision procedure is often necessary. An issuegenerally encountered by surgeons replacing joints during a revisionprocedure is the additional loss of native bone near the joint beingreplaced. This bone loss is typically due to movement of the componentor components after implantation or even degeneration or furtherdegeneration of the bone, which can form bone voids that haveunpredictable and non-uniform shapes. In addition, revision proceduresoften involve the removal of additional bone, which makes maintaining orotherwise restoring the structural integrity often afforded by nativebone of great importance.

For instance, when bone voids are observed in either the proximal tibiaor distal femur, or both, it is standard surgical practice to fill thosevoids as part of the revision surgical procedure. The preferred practiceis to fill those voids with weight bearing void fillers, typically madeof an implant-grade metal such as titanium. However, because the bonevoids are typically irregular in shape, some preparation of the bonevoid area is typically required prior to implantation of the voidfiller. This preparation (typically by reaming, broaching or milling)ensures there is sufficient room in the bone void for the void filler.An accurate fit between the shaped bone void and the void filler is alsoimportant for establishing joint line, and allowing for weight bearingand bone remodeling during the recovery process. Of course, thisprocedure involves the removal of even more native bone, so greatlengths should be taken to minimize the overall amount removed.

Different methods are commonly used to attempt to prepare the bone voidarea to create an accurate fit between the shaped bone void and voidfiller. One method is to ream along the intramedullary (“IM”) axis,followed by broaching. Another method is to ream along the IM axis,followed by freehand burring or rongeur bone removal, which may also befollowed by broaching. Problems with these methods include that reamingis performed on the IM axis only, so that void areas at a distance fromthe IM axis, which commonly occur, can only be resected using manualmethods. Moreover, broaching generally has at least two problems. First,a manual operation can be time consuming, particularly in cases ofsclerotic bone, which exposes the patient to an increased risk ofinfection and longer recovery. Second, in the case of large bone voids,broaching generally needs to be performed in a multi-step processbecause attempting to remove high volumes of bone in a single broachingstep generally requires high impact forces to the bone. Also, freehandbone removal, either powered or unpowered, such as with a burr orrongeur, often does not produce accurate void shapes to receivepredefined prosthetic components. A typical result is that areas remainwhere the outer walls of the void filler do not contact the void, whichmay lead to undesirable stress distribution and possible loss of boneregrowth. Also typical is the time consuming requirement of iterativebone removal, with multiple checks against the void fillers, to obtain acorrect fit.

Occasionally the bone loss or bone deformity is so significant that thesurgeon must resect a portion of bone along its length and supplementthe bone loss with a bone augment. Since the surgeon typically attemptsto preserve as much native bone as possible, the result of the resectionis typically a bone that has multilevel plateaus, where the bone augmentis commonly placed between the joint prosthesis and one plateau in orderto augment the missing bone, and the prosthesis itself is placed againstthe other plateau. However, this resection generally does not eliminatethe need for a void filler. Generally, the bone void extends through themultilevel plateaus, which creates an area where the void filler wouldbe exposed and would interfere with the placement of the bone augmentwhen implanted. Unfortunately, this situation is often unpredictable asthe surgeon is often unaware of the need to augment until the previousprosthesis has been removed.

Thus, there is a need for a bone void filler that is adaptable to beused in both a joint revision procedure requiring a bone augment so asto not interfere with the placement of the augment and a joint revisionprocedure where a bone augment is not needed.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present disclosure, a bone void filling prosthesisincludes a body having a frustoconical profile, a length defined betweena first end and a second end, and an aperture extending through theentirety of the length. The aperture defines a sidewall having athickness spanning between an outer surface and an inner surface of thebody. The void filling prosthesis also has at least one leg having afrustoconical profile, and a first and second end. The at least one legis coupled to and extends away from the body such that the first end ofthe at least one leg is disposed between the first and second ends ofthe body.

Additionally, the at least one leg may have a first surface and a secondsurface. The first surface may be disposed at the second end of the atleast one leg. The first surface may intersect the second surface at anangle, and the angle may be substantially equal to an angle formedbetween two resected surfaces of a femur bone. Further, the at least oneleg may include a bone contact surface and a prosthesis facing surface.The bone contact surface may be formed from a porous material and theprosthesis facing surface being formed from a solid material. The bonecontact surface may intersect the prosthesis facing surface at aprosthesis boundary. The prosthesis boundary may be formed of a solidmaterial such as to form a rim of solid material along the bone contactsurface.

Continuing with this aspect, the at least one leg may include a firstleg and a second leg coupled to the body. The first leg and second legmay each have a frustoconical profile. Further, the first leg may beseparated from the second leg by a space. The space may define a firstinner surface extending along the first leg and a second inner surfaceextending along the second leg. The first inner surface may have aplanar portion and a stepped portion.

Also, the aperture may extend through the thickness of the sidewall fromthe first end to the second end of the body and may further define acurved portion and a first and second wall portions. The curved portionmay have a frustoconical outer surface and a cylindrical inner surface.The curved portion may have an inner radius and the first and secondwall portions may each have a planar inner surface. The first and secondwall portions may be coupled to the curved portion such that the planarinner surfaces of the first and second wall portions are tangent to animaginary cylinder defined by the curved portion. Alternatively, wherethe inner surface of the curved portion is frustoconical, the first andsecond wall portions may be coupled to the curved portion such that theplanar inner surfaces of the first and second wall portions are tangentto an imaginary conical frustrum defined by the curved portion.

In another aspect of the present disclosure, a bone void fillingprosthesis includes a body having a length defined between a first endand a second end, and an aperture extending through the entirety of thelength. The aperture defines a sidewall having a thickness spanningbetween an outer surface and an inner surface of the body. The apertureextends through the sidewall from the first end to the second end.

Additionally, the aperture may define a curved portion and a first andsecond wall portions. The first and second wall portions may beseparated by a distance. The curved portion may have a frustoconicalouter surface and a cylindrical inner surface. Further, the curvedportion may have an inner radius and the first and second wall portionsmay each have a planar inner surface. In one embodiment, the first andsecond wall portions may be coupled to the curved portion such that theplanar inner surfaces of the first and second wall portions are tangentto an imaginary cylinder defined by the curved portion. Alternatively,the first and second wall portions may be coupled to the curved portionsuch that the planar inner surfaces of the first and second wallportions are tangent to an imaginary conical frustrum defined by thecurved portion.

Continuing with this aspect, the bone void filling prosthesis may alsoinclude at least one leg having a first end and second end. The at leastone leg may be coupled to and extend away from the body. The body andthe at least one leg may each have a frustoconical profile.

In a further aspect of the present disclosure, a bone void fillingprosthesis includes a body having a length defined between a first endand a second end, and an aperture extending through the entirety of thelength. The aperture defines a sidewall having a thickness spanningbetween an outer surface and an inner surface of the body. The outersurface is formed of a porous material for promoting bony ingrowth, andthe inner surface is formed of solid material. The the inner surface andouter surface are connected at a boundary of the prosthesis by a rimformed of solid material that extends through the entirety of thethickness and forms at least a portion of the outer surface. The rim mayinclude a channel extending therein for receipt of an adhesive.

In yet another aspect of the present disclosure, a joint replacementsystem includes a void filling prosthesis having a body. The bodyincludes a length defined between a first end and a second end and anaperture extending through the entirety of the length. The aperturedefines a sidewall having a thickness spanning between an outer surfaceand an inner surface of the body. The aperture extends through thethickness of the sidewall at one location throughout the entire lengthof the body and further defines a curved portion and a first and secondwall portions. The curved portion has a radius and the first and secondwall portions are separated by a distance. The system also includes astem component having a cross-sectional thickness smaller than theradius of the curved portion and the distance between the first andsecond wall portions so as to leave about at least a 2 mm gap betweenthe stem component and inner surface of body when the stem component isinserted into the aperture of the body.

Additionally, the first wall portion may define a plane tangent to animaginary circle defined by the curved portion. The curved portion ofthe body may have an outer surface having a frustoconical taper from thefirst end to the second end of the body.

The system may also include a reamer assembly that includes anintramedullary component, a support, and a reamer. The curved portion ofthe body may include an outer surface having a frustoconical taper fromthe first end to the second end of the body. The reamer may include ashaft and a frustoconical head having a taper from a first end to asecond end of the head. The taper may be substantially equal to thefrustoconical taper of the outer surface of the curved portion.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 shows a perspective view of one embodiment of a void fillingprosthesis.

FIG. 2 shows a front view of the void filling prosthesis of FIG. 1.

FIG. 3 shows another perspective view of the void filling prosthesis ofFIG. 1.

FIG. 4 shows a side perspective view of the void filling prosthesis ofFIG. 1.

FIG. 5 shows a top perspective view of another embodiment of a voidfilling prosthesis of FIG. 1.

FIG. 6 shows a bottom perspective view of the void filling prosthesis ofFIG. 5.

FIG. 7 shows a side view of the void filling prosthesis of FIG. 1interfacing with a femoral component.

FIG. 8 shows a rear view of the void filling prosthesis of FIG. 1interfacing with a femoral component.

FIG. 9 shows a side view of the void filling prosthesis of FIG. 5interfacing with a femoral component.

FIG. 10 shows a top perspective view of the void filling prosthesis ofFIG. 5 interfacing with a femoral component.

FIGS. 11-19 show a method and instrumentation for forming a bone void toreceive the prostheses of FIG. 1 and FIG. 5.

FIG. 20 shows a front view of another embodiment of the void fillingprosthesis having selectively removable legs.

FIG. 21 shows a partially schematic perspective view of the void fillingprosthesis of FIG. 20 having an intermediate member.

FIG. 22 shows a partially schematic perspective of the void fillingprosthesis of FIG. 20 absent the intermediate member.

FIG. 23 shows a perspective view of void filling prosthesis of FIG. 20absent a selectively removable leg.

FIG. 24A is a front perspective view of an alternative void fillingprosthesis.

FIG. 24B is a highly schematic cross-sectional view of a leg and aportion of a central body of the void filling prosthesis of FIG. 24Aillustrating a solid rim and porous outer surface.

FIG. 25 is a bottom view of the void filling prosthesis of FIG. 24A.

FIG. 26 is a top perspective view of the void filling prosthesis of FIG.24A.

FIG. 27 is a depiction of the void filling prosthesis of FIG. 24Aimplanted into a femur bone.

FIG. 28A is a front perspective view of yet another void fillingprosthesis.

FIG. 28B is a highly schematic cross-sectional view of a portion of thevoid filling prosthesis of FIG. 28A illustrating a solid rim and porousouter surface.

FIG. 29A is a front perspective of a further void filling prosthesis.

FIG. 29B is an alternative embodiment of the void filling prosthesis ofFIG. 29A.

DETAILED DESCRIPTION

When referring to specific directions in the following discussion ofcertain implantable devices, it should be understood that suchdirections are described with regard to the implantable device'sorientation and position during exemplary application to the human body.Thus, as used herein, the term “proximal” means close to the heart andthe term “distal” means more distant from the heart. The term “inferior”means toward the feet and the term “superior” means toward the head. Theterm “anterior” means toward the front of the body or the face and theterm “posterior” means toward the back of the body. The term “medial”means toward the midline of the body and the term “lateral” means awayfrom the midline of the body. Also, as used herein, the terms “about,”“generally” and “substantially” are intended to mean that slightdeviations from absolute are included within the scope of the term somodified.

FIGS. 1-4 depict a first embodiment of a void filling prosthesis 10. Thevoid filling prosthesis 10 includes a central body 11, a medial leg 13,and a lateral leg 12. In another embodiment, the void filling prosthesis10 may include a central body and only a medial leg 13 or lateral leg12. The central body 11 is generally cylindrical. However, thiscylindrical shape may take the form of a portion that has a constantdiameter and a portion that is slightly tapered such that it isgenerally frustoconical. The central body 11 includes an aperture 18that extends through the central body 11 in order to allow the passageof an IM stem of a femoral component 30. This aperture 18 forms a wall19, which is integrated with the lateral and medial legs 12, 13 forminga monolithic structure.

The lateral and medial legs 12, 13 may be offset posteriorly from amedian transverse axis of the central body 11. Further, the lateral andmedial legs 12, 13 may be located in close proximity, but may beseparated generally by a space 17 that penetrates through both legs andforms a saddle-like structure in order to provide clearance for afemoral cam box 33 of a femoral component 30. This space 17 forms innersurfaces 15 a-d that abut the femoral cam box 33 when implanted. Theseinner surfaces 15 a-d may be flat, planar walls, or they may be steppedto provide surfaces conducive for bonding with bone cement. Further,inner surface 15 d may be obliquely angled with respect to thelongitudinal axis of the central body 11 in order to account for theangle of the IM stem (not shown) with respect to the cam box.

Further geometric features may be incorporated into the medial andlateral legs 12, 13 in order to provide clearance for the structure ofthe femoral component 30. For instance, inclined surfaces 14 a-d may befashioned into each leg in order to provide clearance for a boneinterface surface 35 of the femoral component 30.

The remainder of the lateral and medial legs 12, 13 that has not beenshaped to form clearance space is depicted as having a generallyfrustoconical profile. This geometric profile is preferred in order toconform more closely to bone voids created by the reaminginstrumentation. However, this is merely an example of a geometry thatthe medial and lateral legs 12, 13 may form. The legs 12, 13 may haveother geometries, such as box-like geometries. Further, the medial andlateral legs 12, 13 may be symmetric with respect to one another, orthey may be asymmetric where one leg 12, 13 may be larger than the other12, 13 and/or one leg 12, 13 may have a different geometry. A conicalstructure 16 a-b may be disposed at one end of each of the lateral andmedial legs 12, 13. This conical structure 16 a-b may help preventrotation of the prosthesis 10 when implanted in the bone and help theprosthesis 10 settle into the proper orientation and more closelyconform to the void formed by the reaming instruments.

Referring to FIGS. 1-4 and 7-8, each leg 12, 13 is shown to include tworemovable portions 20 a-d at an end of each leg 12, 13. While tworemovable portions 20 a-d are shown, this is merely an example. Each leg12, 13 may include any number of selectively removable portions 20 a-d,including just one. Alternatively, one leg 12, 13 may include at leastone selectively removable portion 20 a-d while the other leg 12, 13 mayhave no selectively removable portions 20 a-d. Where one or moreselectively removable portions 20 a-d is removed from a leg 12, 13, thelength of the leg 12, 13 is decreased in order to make room in the jointcavity for a bone augment, for example. This removability provides theoperator the operating room capability and flexibility to configure thevoid filling device 10 to work in conjunction with a bone augment, oralternatively work where no augment is needed. Thus, each selectivelyremovable portion 20 a-d is shaped to conform to the geometries of thevoid filling prosthesis 10 as though they will never be removed.Further, where these portions 20 a-d are not removed, they providestructural support to the prosthesis 10.

Where there are multiple selectively removable portions 20 a-d, they arelayered along the length of each leg 12, 13 as far as needed toaccommodate a bone augment. Each selectively removable portion 20 a-dmay have a first section 22 a-d made from a weaker material and a secondsection 21 a-f made from a stronger material, where the two sections 21a-f, 22 a-d are layered along the length of each leg 12, 13.

In a preferred embodiment, the weaker and stronger material may be madefrom the same metallic material, but the weaker material may have ahigher porosity than that of the stronger material allowing for aseamless transition between these two sections 21 a-f, 22 a-d, butproviding a region for easy separation. Separation is made easier by thefact that the more porous material is easier to separate and that thetwo sections 21 a-f, 22 a-d are visually recognizable indicating theseparation location.

In one embodiment, the separation location may be designated by a smallchamfer to receive a cutting blade between the first section 22 a-d ofone selectively removable portion 20 a-d and the second section 21 a-fof another selectively removable portion 20 a-d. An example of theporous metallic material may be titanium, titanium alloy, stainlesssteel, cobalt chrome alloys, tantalum or niobium formed by SelectiveLaser Melting (“SLM”) as described in U.S. Pat. No. 7,537,664 titled“Laser-Produced Porous Surface,” the entirety of which isincorporated-by-reference herein fully set forth herein and which isassigned to the same entity as the present invention. Additionalexamples are disclosed in U.S. Application Nos. 11/027,421, filed Dec.30, 2004, Ser. No. 11/295,008, filed Dec. 6, 2005, and Ser. No.13/441,154, filed Apr. 6, 2012, and U.S. Pat. Nos. 8,350,186 and8,147,861, the entireties of which are incorporated-by-reference hereinas if fully set forth herein.

In an alternative embodiment, the weaker material may have the sameporosity as the stronger material, but may be constructed from amaterial that has a lower modulus than the stronger material. In anotherembodiment, the entire void filling prosthesis 10 may be constructedfrom a porous metallic material including the selectively removableportions 20 a-d with little or no variations in the porosity, but thatthe selectively removable portions 20 a-d have score marks to designatethe cutting points. In a further embodiment, the first section 22 a-dmay have an outer shell that is the same porosity as the remainder ofthe void filling prosthesis 10, and an interior portion constructed fromthe weaker material.

These selectively removable portions 20 a-d may be removed by cuttingalong the weaker section 22 a-d generally parallel and adjacent thestronger section 21 a-f of another selectively removable portion 20 b,20 d that is more proximate the central body using a cutting device. Forinstance a cutting device may be a guillotine-like device, an example ofwhich is disclosed in U.S. application Ser. No. 12/002,002, filed Dec.13, 2007, the entirety of which is incorporate-by-reference herein as iffully set forth herein. Where the selectively removable portion 20 b, 20d is the last selectively removable portion along the length of thatparticular leg 12, 13, the leg 12, 13 may have a layer of strongermaterial 21 c, 21 f just adjacent to the weaker section 22 b, 22 d ofthat selectively removable portion 20 b, 20 d to facilitate removal.

The remainder of the void filling prosthesis 10 may also be partiallyconstructed from porous metallic material as described above. In oneembodiment, the surfaces in contact with the femoral component 30, suchas internal surfaces 15 a-d, may be constructed of solid metallicmaterial, such as titanium as an example, while the remainder of thevoid filling prosthesis 10 may be constructed of porous metallicmaterial.

FIGS. 5 and 6 depict an alternative embodiment wherein the bone voidfiller 10′ does not include selectively removable portions 20 a-d, buthas substantially the same geometries as prosthesis 10. This embodimentmay also be constructed from the same materials as that of prosthesis10, including portions of porous metallic material. Further, thisembodiment may also be constructed from solid metal or high strengthpolymeric material.

FIGS. 7-10 depict the interface between the void filling prosthesis 10,10′ and a femoral component 30. The femoral component 30 may be anyfemoral component 30, for example a femoral component 30 utilized in aposterior stabilized or total stabilized total knee prosthesis, forexample the Scorpio® TS femoral component (Howmedica Osteonics, Mahwah,N.J.).

The void filling prosthesis 10, 10′ may be placed in contact with thefemoral component such that aperture 18 of the central body 11 is placedover a stem portion of the femoral component 30 and the inner surfaces15 a-d are placed in contact with the cam box 33. In one embodiment,bone cement is placed between the inner surfaces 15 a-d and the cam box33 to provide for additional support. Such inner surfaces 15 a-d may bestepped to provide more surface area for bonding to the cement.

In one embodiment, the distal ends of the legs 12, 13 do not contact thebone contacting surface 35 of the femoral component in order to providesome space for bone cement to flow and to provide space so that theoperator can make minor corrections to the rotation of the femoralcomponent 30.

A set of guided instruments may be provided to form the bone void toreceive the void filling prosthesis. Included in this set of instrumentsmay be an IM reamer 40, a boss reamer 50, a reamer guide assembly 60, analignment handle 90, an alignment pin 100, a lobe reamer assembly 110,and a lobe trial 120.

The IM reamer 40, as depicted in FIG. 11, may include a shaft 42 thatincludes a plurality of depth indicators 44 situated along the length ofthe shaft 42 at designated intervals, and a reamer head 43 disposed atone end of the shaft. The other end of the shaft 41 may be configured tointerface with a torque applying device, such as the chuck of a drill.

The boss reamer 50, as depicted in FIG. 12, may include a cannulatedshaft 52 that includes a boss reamer head 53 at one end. The other end51 of the shaft 52 may be configured to interface with a torque applyingdevice, such as the chuck of a drill. The internal diameter of thecannulated shaft 52 is such that the shaft 52 may be slid over the IMreamer shaft, but generally not the IM reamer head, and rotated withrespect to the IM reamer. The boss reamer head may also be cannulated toslide over the IM reamer shaft 42 and may have a cutting diametersubstantially similar to the diameter of the central body 11.

The reamer guide assembly 60, as depicted in FIGS. 13-19, may include atrial stem 70 and a reamer guide 80. The reamer guide generally includesa base 82, a support shaft 81, and a guide block 88. The trial stem 70may be connected to one end of the base 82. In one embodiment, thisconnection may be a threaded connection, ball-detent connection or anyother connection as is known in the art. The other end of the base 82includes an abutment surface 89 and the support shaft 81 extending fromthe base 82 at an outward angle with respect the longitudinal axis ofthe trial stem 70. The support shaft 81 then bends such that theremainder of the support shaft 81 is generally parallel to thelongitudinal axis of the trial stem 70. Integrated into the end of theguide shaft 81 is the guide block 88. The guide block 88 generallyincludes a handle hole 83 extending through the guide block 88 forreceipt of an alignment handle 90 (described below), an alignmentpinhole (not shown) for receipt of an alignment pin 100 (describedbelow), and a first and second lobe reamer guide 84, 85. The first andsecond lobe reamer guides 84, 85 are generally disposed between thehandle hole 83 and alignment pinhole. Both the first and second lobereamer guides 84, 85 include a passageway 86 a, 86 b that issubstantially cylindrical and a side-slot 87 a, 87 b extending throughthe sides of each of the lobe reamer guides 84, 85 into the passageway86 a, 896 b. The longitudinal axes of the passageways 86 a, 86 b extendto a location on the abutment surface 89. Further, these longitudinalaxes may be provided at various angles with respect to the longitudinalaxis of the trial stem 70 in order to ream different bone voiddimensions.

The alignment handle 90, as depicted in FIG. 14-19, is generally anelongate shaft with a flange disposed 91 along its length for abuttingagainst the guide block 88. The alignment pin 100 is preferably a ⅛″diameter pin with a length long enough to extend beyond the epicondyleswhen inserted into the guide block 88. While ⅛″ diameter is preferred soas to not obstruct the epicondyles from the operator's view, anydiameter pin may be used.

The lobe reamer assembly 110, as depicted in FIGS. 15-17 and 19,includes a lobe reamer head 117, a reamer shaft 116, a depth stop collar112, and a bushing 113. The lobe reamer head 117 is disposed at one endof the reamer shaft 116, while the other end 111 of the shaft 116 isconfigured to interface with a torque applying device. The depth stopcollar 112 is fixed to the reamer shaft 116 opposite the end of the lobereamer head 117. The reamer shaft 116 has a diameter small enough to fitthrough the side-slot 87 a, 87 b of the first and second reamer guides84, 85. The bushing 113 is disposed along a portion of the reamer shaft116 between the reamer head 117 and depth stop collar 114 such that thebushing 113 can slide back and forth between the reamer head 117 anddepth stop collar 112. The bushing 113 is generally cylindrical andincludes a first segment 115 and second segment 114 where the secondsegment 114 generally has a larger diameter than the first segment 115.The diameter of the first segment 115 may be dimensioned to slide intoand fit tightly within the passageway 86 a, 86 b of the first and secondlobe reamer guides 84, 85.

The lobe trial 120, as shown in FIGS. 18 and 19, includes a lobe trialhead 125 and a first shaft segment 124 and a second shaft segment 122.The lobe trial head 125 d is disposed at the end of the first shaftsegment 124 and generally has a frustoconical shape with a portionremoved along its length. The lobe trial head 125 is dimensioned tosubstantially match the bone void formed by the reamer head 116 and tosubstantially match at least one leg 12, 13 of the void fillingprosthesis 10. While the lobe trial head 125 is depicted as having thisshape, the lobe trial head 125 may have any shape depending on the shapeof the reamer head 116 and the legs 12, 13 of the void fillingprosthesis 10. The first shaft segment 124 has a diameter less than thatof the second shaft segment 122 and is dimensioned to be capable ofpassing through the side-slot 87 a, 87 b of the first and second lobereamer guides 84, 85. The second shaft segment 122 is dimensioned suchthat it can tightly fit and slide within the passageway 86 a, 86 b ofthe first and second lobe reamer guides 84, 85. An impact surface 121 isformed at the opposite end of the lobe trial 120 as that of the lobereamer head 125. The impact surface 121 is a relatively broad andflattened surface so that the operator can impact the lobe trial 70 inorder to seat the lobe trial head 125 into a bone void.

In one embodiment of the present invention, a method for forming a voidin bone to receive the void filling prosthesis 10, as illustrated byFIGS. 11-19. In this embodiment, the instruments, as described above,are utilized. While FIGS. 11-19 and the following description of themethod are directed toward the preparation of a bone void within afemur, it is to be understood that this is merely an example. Thefollowing method may be utilized to prepare a bone void in any longbone.

Referring to FIG. 11, the IM reamer 40 is depicted as reaming along theIM canal of a femur 200 until the bone 200 is flush with the requisitedepth indicator 44. While it appears from FIG. 11 that the IM reamer 40is passing through a femoral component, the femoral component is merelya depiction of the femur 200. With the IM reamer 40 remaining within theIM canal, the boss reamer 50 is slid over the shaft of the IM reamer, asshown in FIG. 12. The operator reams along the IM reamer shaft 42 untilthe boss reamer head 53 abuts the IM reamer head 40, thereby preventingfurther travel into the femur bone 200. The IM reamer and boss reamer 50are then removed from the IM canal in preparation for further boneforming.

Referring to FIG. 13, the reamer guide assembly 60 is assembled. In suchassembly, the operator may select a trial stem 70 to match the IM reamerhead diameter, and then attach the trial stem 70 to the reamer guide 80.In another embodiment, the IM reamer 40 may be attached to the reamerguide 80, thus taking the place of the trial stem 70. Attachment may beby a threaded engagement, with a ball detent, or any other engagementknown in the art. Once the reamer guide assembly 60 is assembled, thetrial stem 70 is inserted into the portion of the IM canal that wasreamed by the IM reamer 40, and the base of the reamer guide 82 isinserted into the portion of bone reamed by the boss reamer 50. Theoperator may further seat the reamer guide assembly 60 to the properdepth by impacting the end of the guide block 88. The proper depth maybe indicated when the reamer guide assembly 110 no longer moves whenimpacted and generally where the bone is flush with the bend in thesupport shaft 81.

Referring to FIG. 14, with the reamer guide assembly 60 firmly seatedwithin the IM canal, the alignment handle 90 is placed in the handlehole 83 until the flange 91 abuts the guide block 88, and the alignmentpin 100 is placed in the alignment pinhole such that the alignment pin100 extends from both sides of the guide block 88 beyond the peripheryof the femur. The operator will then grip the alignment handle 90 androtate the reamer guide assembly 60 within the IM canal until thealignment pin 100 is aligned with the transepicondylar axis or any axisof the operator's preference.

Referring to FIG. 15, once alignment is achieved the lobe reamerassembly 110 is loaded into the first lobe reamer guide 84. This isachieved by moving the bushing 113 so that it abuts the depth stopcollar 112, thereby exposing the reamer shaft 116 proximate to thereamer head 117. The reamer shaft 116 is then side-loaded through theside-slot 87 a and into the passageway 86 a. The resulting configurationshould be such that the reamer head 116 is located on one side of thefirst lobe reamer guide 84 and the bushing 113 located on the otherside, as shown in FIG. 15. The first segment 115 of the bushing 113 isthen slid into the passageway 86 a until the second segment 113 abutsthe first lobe reamer guide 84, as shown in FIG. 16. The reamer head 116is then advanced into the distal femur by applying a torque to thereamer shaft 115 until the depth stop collar 112 abuts the bushing 113and the reamer head 116 abuts the abutment surface 82, as shown in FIG.17. The reamer head 116 is then retracted from the femur and the reamerassembly 110 removed from the first lobe reamer guide 84 through theside-slot 87 a.

Referring to FIG. 18, the lobe trial 120 is then loaded into thepassageway 86 a of the first lobe reamer guide 84 in a similar fashionas the lobe reamer assembly 110. The first shaft segment 124 of the lobetrial 120 is passed through the side-slot 87 a and into the passageway86 a. The lobe trial head 125 is then advanced into the first bone void.As the lobe trial head 125 is advanced, the second shaft segment 123 isadvanced into the passageway 86 a and the lateral protrusion 123 isadvanced into the side-slot 87 a. The lateral protrusion 123 ensuresthat the lobe trial 120 has the proper rotational alignment and alsoacts as a stop to prohibit rotation. In one embodiment of the lobe trial120, the lateral protrusion 123 may be a pin that extends through thesecond shaft segment 122 and into a hole located in the first lobereamer guide 84 to prevent both rotational and translational movement.The operator may then impact the impact surface 121 to fully seat thelobe trial 120. The lobe trial 120 may remain in place while a secondbone void is formed in order to provide additional stability duringreaming, as seen in FIG. 19.

Referring to FIG. 19, the lobe reamer assembly 110 is side-loaded intothe second lobe reamer guide 85 as previously described. The reamer head117 is then advanced into the distal femur by applying a torque to thereamer shaft 116 until the depth stop collar 112 abuts the bushing 113and the reamer head 117 abuts the abutment surface 89, thereby forming asecond bone void for receipt of the void filling prosthesis 10.

While this method has generally been described herein as utilizing onelobe reamer assembly 120 to form both bone voids, more than one lobereamer assembly 110 having different geometries may be used depending onthe geometry of the void filling prosthesis 10.

FIGS. 20-23 depict another embodiment void filling prosthesis 210, whichis similar to the void filling prosthesis 10 previously described butdiffers in that an entire leg may be selectively removed.

As shown, void filling prosthesis 210 includes a central body 211, alateral leg 212 and medial leg 213. Central body 211 is shown as beinggenerally cylindrical and including an aperture 218 extendingtherethrough, like in the void filling prosthesis embodiments previouslydescribed herein. The central body 211 can be made from variousmaterials including titanium, titanium alloy, stainless steel, cobaltchrome alloys, tantalum, or niobium. In addition, these materials may beprovided in various forms, such as in a solid or porous form, forexample, in the form of metallic foam.

In a preferred embodiment, the central body 211 includes an inner sleeve217 (best shown in FIGS. 20 and 23) constructed from a solid materialand an outer shell 216 (best shown in FIGS. 21 and 22) constructed fromthe same material in porous form to facilitate bony ingrowth. As anexample, the inner sleeve 217 may be constructed from solid titanium andthe outer shell 216 may be constructed from titanium foam. The innersleeve 217 is generally the inner support structure for the centralbody, with the solid construction of the inner sleeve 217 providingstructural support to a porous outer shell 216 and a bearing surface foran implant stem (not shown).

In other embodiments, the central body 211 can be constructed entirelyof one material in one form. For example, the central body 211 may beconstructed entirely of a solid titanium or titanium foam. In anotherembodiment, the central body 211 may be constructed from differentmaterials and different forms. For example, the inner sleeve 217 can beconstructed from solid tantalum and the outer shell 216 can beconstructed from titanium foam.

Central body 211 also includes a first end, a second end and anintermediate member 214 coupled to the second end. In some embodiments,intermediate member 214 may be a separate structure mechanically coupledto the second end of the central body 211, for example via a weldedconnection or an adhesive. In other embodiments, the intermediate member214 may be integrated into the central body 211 to form a monolithicstructure, for example by building both structures togetherlayer-by-layer or molding the structures together as a unitarystructure. In either embodiment, the intermediate member 214 ispreferably sized and shaped to conform substantially to the central body211 such that there may be a smooth transition between the intermediatemember 214 and central body 211.

The intermediate member 214 can be constructed from the same materialsand forms as that previously discussed in relation to the central body211. In a preferred embodiment, the intermediate member 214 isconstructed from a porous material that has a porosity larger than thatof the outer shell 216 of the central body 211. Generally, theintermediate body's construction is selected to facilitate connection oflegs 212 and 213 to the central body 211 and to allow for ease ofseparation of legs 212 and 213 from the central body 211 when desired.As such, the porous material used in constructing the intermediatemember 214 may include spaces or cells (not shown) that are both largerelative to that of the central body's materials and predeterminatelyarranged in a uniform pattern, rather than randomly distributedthroughout the material. This uniform pattern and large porosityrelative to that of the central body 211 may facilitate penetration of acutting device and provide for a smooth and uniformly cut surface. Inone example, the cells of the porous material can be polygonal like thatof a honeycomb or like a hollow rectangular prism. Thus, in oneembodiment, the intermediate member can be constructed from titaniumhoneycomb or from titanium arrayed with adjacently situated, hollowrectangular prisms. These polygonal-like cells may provide structuralstrength while allowing the walls (not shown) making up each cell to bethin to facilitate ease of cutting.

In an alternative embodiment, the intermediate member 214 can beconstructed from a metallic material with a lower modulus to that of thecentral body 211 and/or lateral and medial legs 212, 213 to facilitateease of cutting and to help prevent cutting penetration of the centralbody 211 and/or the lateral and medial legs 212, 213. In anotherembodiment, the intermediate member 214 may have an identicalconstruction to that of the central body 211 or be made entirely frommetallic foam.

The lateral and medial legs 212, 213 have a similar profile to thelateral and medial legs 12, 13 previously described herein in order toconform to predictably shaped bone voids formed by generally cylindricalreamers and to communicate with a femoral component. Each leg 212, 213is formed by a portion or portions of a support member 220 (discussedmore fully below) covered with a bone interface member 230.

As best shown in FIGS. 21 and 22, the support member 220 includes anupper portion 222, a middle portion 224, a lower portion 226, an innersurface 228 and outer surface 229. In some embodiments, the supportmember 220 may only include the upper portion 222 and middle portion224, or may only include the upper portion 222. As depicted, the upperportion 222 and lower portion 226 join the middle portion 224 to form az-like configuration. The upper portion 222 is semi-cylindrical and hasan inner radius similar to the inner radius of the intermediate member214. The middle and lower portion 224, 226 are preferably dimensionedand shaped to conform to the periphery of the bone interface member 230.

The bone interface member 230 generally interfaces with the bone whenimplanted, while the support member 220 generally communicates with afemoral component when implanted and supports the bone interface member230 in a connection with the central body 211 via the intermediatemember 214. The support member 220 includes generally planar inner andouter surface 228, 229 to make way for the femoral component, and thebone interface member includes generally curved surfaces to conform tothe bone.

In some embodiments, the bone interface member 230 may be a separatestructure mechanically coupled to the inner surface 228 of the middleand lower portions 224, 226 of the support member 220. In otherembodiments, the bone interface member 230 may be integrated into thesupport member 220 to form a monolithic structure, for example bybuilding both structures together layer-by-layer or molding thestructures together as a unitary structure.

The lateral and medial leg 212, 213 can be constructed from any of thematerials and forms previously described in relation to the central body211 and intermediate member 214. In a preferred embodiment, the supportmember 220 of each leg is constructed from a solid material and the boneinterface member 230 is constructed from a porous material. As anexample, the support member 220 may be made from solid titanium, and thebone interface member 230 may be made from titanium foam.

In an alternative embodiment, the support member 220 and bone interfacemember 230 may be made from one material in one form. For example, thesupport member 220 and bone interface member 230 may be made entirelyfrom metallic foam. In another embodiment, the support member 220 andbone interface member 230 of each leg 212, 213 can be constructed fromdifferent materials and different forms. For example, the support member220 may be made from solid tantalum while the bone interface member 230may be constructed from titanium foam. In yet another embodiment, thelateral and medial leg 212, 213 may be constructed as that previouslydescribed in relation to void filling prosthesis 10, wherein the lateraland medial legs 212, 213 include selectively removable portions forreducing the length of a select leg.

The upper portion 222 extends outwardly from its respective leg 212, 213in a cantilevered fashion and is coupled to the intermediate member 214at the inner surface 228 of the upper portion 222. Such connectionoccurs substantially along a plane to facilitate separation between theintermediate member 214 and the upper portion 222, which may result inthe removal of a leg. Separation may also be facilitated by a gap 215formed between the upper portion 222 of the lateral leg 212 and theupper portion 222′ of the medial leg 213, which allows separation of asingle leg to occur by cutting along a single plane. In other words, thelateral leg 212 and medial leg 213 may be separate structures attachedto the intermediate member 214, with a gap 215 formed therebetween. Incertain embodiments, the legs 212, 213 may be formed as a unitarystructure in that both legs 212, 213 may be directly connected to eachother with no gap being formed. In such a case, where it would bedesirable to remove only the lateral leg 212 or only the medial leg 213,separation may be achieved by cutting between the intermediate member214 and upper portion 222 as well as at a location somewhere between thelateral and medial leg 212, 213 in order to remove the leg. On the otherhand, where the legs 212, 213 are separate structures forming a gap 215,separation may be achieved by cutting only between the intermediatemember 214 and upper portion 222.

Additionally, gap 215 may extend into the intermediate member 214 orbisect the intermediate member 214. The extension of the gap 215 intothe intermediate member 214 or bisection of the intermediate member 214by the gap 215 may allow the operator to cut the intermediate member 214along any plane extending through the intermediate member 214 to the gap215, rather than only along a plane formed by the junction of theintermediate member 214 and each leg 212, 213.

Generally a lateral or medial leg 212, 213 may be removed through theuse of a cutting device, such as that previously discussed herein anddisclosed in U.S. application Ser. No. 12/002,002, the disclosure ofwhich is hereby incorporated by reference herein, by cutting in ananterior-posterior direction. In some embodiments the bone interfacemember 230 may wrap around a portion of the intermediate member 214partially obstructing the intermediate member 214 anteriorly and/orposteriorly as depicted in FIGS. 20 and 23. In such embodiments, theupper portion 222 of the support member 220 may attach to theintermediate member 214 at locations that are not obstructed by the boneinterface member as illustrated in FIGS. 21 and 23, allowing ananterior-posterior cut to be performed along the junction between theintermediate member 214 and the upper portion 222 without going throughor around the bone interface member 230.

While the aforementioned description and related figures describe a voidfilling device having selectively removable legs, it is contemplatedthat the selectively removable features of the first embodiment 10 maybe combined with selectively removable lateral and medial legs of thepresent embodiment 210 providing an operator with the flexibility toreduce the length of a leg or entirely remove a leg.

Another aspect of the present disclosure includes methods of fillingbone voids. During a knee revision procedure, an operator may remove thepreviously implanted prostheses. Generally, a central bone void extendsinto femur and/or tibia, and oftentimes unpredictably shaped bonedeformities are formed adjacent to the central bone void by theincidental removal of bone during the implant removal process. Such bonedeformities may interfere with the revision prostheses and may berectified in a number of different ways including reaming the bonedeformities to form predictably shaped offset bone voids as previouslydescribed herein and/or by removing a section of bone housing thedeformity from the proximal tibia or distal femur.

Once the bone is shaped to account for bone deformities, the operatormay assess the bone to determine the number of offset bone voids forfilling with a void filling prosthesis. In some instances where thereare less offset bone voids than there are legs associated with a voidfilling prosthesis 210, for example where only a lateral or only amedial offset bone void exists, the operator can remove a lateral ormedial leg 212, 213 in order to correspond with the number of voids.

Generally, a cutting device, such as that previously discussed hereinand disclosed in U.S. application Ser. No. 12/002,002, may be utilizedto separate either the lateral or medial leg 212, 213 from the remainderof the void filling prosthesis. A planar blade may be inserted throughthe junction between the intermediate member 214 and the upper portion222 and between the gap 215 and bone interface portion 30.Alternatively, the planar blade may be inserted through the intermediateportion 214 between the gap 215 and bone interface portion 230. The legmay be removed by cutting from an anterior and/or posterior direction.As previously mentioned, the intermediate member 214 is generallyconstructed of a softer material or a material with a larger porositythan the support member to facilitate visualization of the junctionbetween the two members and to facilitate a smooth and easy cutresulting in a predictable surface.

Once the void filling prosthesis 210 has the desired number of legs, theoperator may implant the prosthesis by inserting the central body 211into a central bone void and the remaining leg(s) into the offset bonevoid(s).

Alternatively, where the offset bone voids equal the number of legs ofthe prosthesis as provided, the implant may be implanted without anyremoval of legs. On the other hand, where there are no offset bonevoids, all of the legs may be removed and the central body 211 andintermediate member 214 may be inserted into the central bone void.

FIGS. 24A-27 depict alternative void filling prosthesis 300. Voidfilling prosthesis 300 is similar in certain respects to void fillingprostheses 10 and 210. For example, prosthesis 300 similarly includes acentral body 302, a first leg 304 and a second leg 306. Alternatively,prosthesis 300 may include a central body 302 and only the first leg orsecond leg 304, 306. Further, void filling prosthesis 300 can similarlyfill a void formed by the methods previously described herein withrelation to FIGS. 11-19. However, prosthesis 300 differs from prostheses10 and 210 with respect to certain features and configurations of thecentral body and first and second legs.

Unlike central bodies 11 and 211, which are depicted as being ring-likeor annular shaped such that each have an enclosed or encompassingcircumference, central body 302 is open. This open central body 302 isdefined by an aperture 308 that extends through the length of the body302 and also through a sidewall along the body's entire length, whichforms a “C” or “U” shaped cross-sectional profile. As such, central body302 includes a curved portion 313 and a first wall portion 315 andsecond wall portion 317, which each adjoin the curved portion 313 atopposite locations. The curved portion 313 may be semicylindrical suchthat it has a constant outer and/or inner radius along the length of thecentral body 302. Alternatively, and preferably, the curved portion 313has a frustoconical taper such that its outer and/or inner radiusdiffers along its length. In some embodiments, the inner radius may beconstant along the length of the body 302, while the outer radius mayhave a frustoconical taper, and thus a varying wall thickness, along thelength of the body 302. In other embodiments, the central body 302 canhave both a cylindrical portion and a frustoconical portion in a stackedarrangement.

The first and second wall portions 315, 317 may have planar inner andouter surfaces such that the cross-sectional profile of the inner andouter surfaces of the central body is U-shaped. In other embodiments,the first and second wall portions 315, 317 may each have a curved outersurface and a planar inner surface which may tangentially intersect animaginary cylinder or conical frustrum defined by the inner surface ofthe curved portion 313. Thus, in such embodiment, the wall thicknessbetween the inner surface and outer surface of the central body 302 atthe first and second wall portions 315, 317 may vary in order to allowfor such planar inner surfaces and curved outer surfaces. Thecross-sectional profile of the outer surface body 302 in such embodimentwould be C-shaped, and the cross-sectional profile of the inner surfaceof the body 302 would be U-shaped. In another embodiment, the inner andouter surfaces of the body 302 at the first and second wall portions315, 317 may be similarly curved such that the cross-sectional profileof the inner and outer surfaces of the body 302 may be C-shaped. Theinner surface of the central body 302 may have three dimensionalfeatures, such as a stepped surfaces, to promote the securement of bonecement or other adhesives thereto. Where such features are included, theinner radius of the curved portion 313 is determined by the innermostregions of such features.

The radius of the curved portion 313 and the shortest distance betweenthe first and second wall portions 315, 317 may be larger than thecross-sectional thickness of a stem 360 of a joint prosthesis such as toallow the placement of about at least a 2 mm cement mantle between thestem 360 and the inner surface of the central body 302. The aperture 308of the central body 302 preferably extends through the sidewall in ananterior direction. However, the aperture 308 may extend through thesidewall in a posterior direction. The combination of the anterior orposterior opening in the sidewall along with dimensioning that allowsfor the placement of a cement mantle provides for the accommodation ofmany different size and shape stem components. Additionally, the spaceprovided by the relatively larger dimensioning and the anterior orposterior opening in the sidewall provides operating-room flexibility inthat it allows the operator to shift the stem 360 and joint prosthesisattached thereto in any number of directions so that the operator canmore precisely position the articular surface of the joint prosthesis.In particular, the flexibility to shift the stem 360 in ananterior-posterior direction is beneficial in positioning the articularsurface in order to achieve the desired flexion and extension gaps andto achieve the desired patellar tendon tension. Such flexibility alsoallows the operator to utilize offset stems without having to refit anew void filling prosthesis.

Similar to the legs of prosthesis 10 and 210, the first and second legs304, 306 may be offset posteriorly from a median transverse axis of thecentral body 302. Further, the first and second legs 304, 306 may belocated in close proximity, but may be separated generally by a space310 that penetrates through both legs and forms a saddle-like structurein order to provide clearance for a femoral cam box of a femoralcomponent. This space 310 forms inner surfaces 320 and 322 that may abutthe femoral cam box when implanted. As best shown by FIGS. 24A and 25,these inner surfaces include flat, planar sections 321, and steppedsections 323 to facilitate bonding with bone cement or other adhesive.Alternatively, these inner surfaces 320, 322 may only be planar and mayinclude a textured surface for cement adhesion, or they may be entirelystepped. Further, inner surface 322 may be obliquely angled with respectto the longitudinal axis of the central body 302 in order to account forthe angle of the IM stem 360 with respect to the surfaces of the cam box(not shown).

Further geometric features may be incorporated into the first and secondlegs 304, 306 in order to provide clearance for the structure of thefemoral component and to also conform to the resected surfaces of thedistal end of a femur bone so as to provide structural support to thebone as close to its outer boundaries as possible. For instance, eachleg includes surfaces 314, 316, and 318, where each surface is angledwith respect to each other such that, when implanted, such surfaceswould be substantially coplanar to a distal, anterior chamfer, andanterior resected surfaces, 352, 354, 356, respectively (best shown inFIG. 27). These surfaces 314, 316, 318 are angled to coplanarly conformto these resected surfaces 352, 354, 356 that are formed in a typicalfive-cut femur (distal, anterior, posterior, and anterior/posteriorchamfer resections). However, each leg 304, 306 could also have surfacesformed to coplanarly conform to a three-cut femur (distal, anterior, andposterior resections). For instance, surfaces 318 and 316 may becombined into one surface angled with respect to surface 314 in order tomatch the angle of an anterior resection with respect to a distalresection of a three-cut femur.

As shown, surfaces 316 and 318 are stepped to facilitate cementedfixation with a femoral joint prosthesis. Surface 314 is planar, but maybe stepped and/or include a textured surface to facilitate cementadhesion. In some embodiments, each of these surfaces 314, 316, 318 maybe planar, or any combination of stepped and planar.

Each leg 304, 306 also includes an impaction feature 324 that is arecess extending longitudinally into each leg 304, 306 from the distalend of each leg. These features are shaped to receive a complementaryshaped impaction tool (not shown) that can tightly fit with theimpaction feature 324 and allow the operator to uniformly impactprosthesis 300 into a void formed in the end of a bone.

The remainder of the first and second legs 304, 306 that has not beenshaped to receive an impaction tool, conform to a femoral cam box, orconform to resected bone surfaces generally has a frustoconical profile.This geometric profile is preferred in order to conform closely to bonevoids created by complimentary frustoconical reaming instrumentation.This frustoconical shape is additionally beneficial in that it allowsfor easy bone preparation utilizing a frustoconical reamer, and alsoprovides a tapered bone contact surface, which facilitates a very tightpress-fit fixation within the target bone. Additionally, thefrustoconical profile of each leg can be the same as the frustoconicalprofile of the central body so that a single reaming device may beutilized to form the bone void to receive prosthesis 300.

However, frustoconical is merely an example of the type of geometry thatthe first and second legs 304, 306 may form. The legs 304, 306 may haveother geometries, such as box-like geometries. Additionally, the firstand second legs 304, 306 may be symmetric with respect to one anotherfor universal fit into both a right and left limb, or they may beasymmetric where one leg 304, 306 may be larger than the other and/orone leg may have a different geometry for a limb specific configuration.

Void filling prosthesis 300 may be constructed from various metallic orpolymeric biocompatible materials. For example, prosthesis 300 can bemade from titanium, stainless steel, cobalt-chromium, tantalum, niobium,or polyethylene. Additionally, prosthesis 300 can have porous outersurfaces 326 for directly contacting bone to facilitate bony ingrowthinto its porous structure. Preferably a portion of prosthesis 300 isformed from porous material and a portion is formed from solid material.Solid, as used herein, means that the porosity of its structure isunlikely to allow bone ingrowth therein.

As best seen in FIGS. 24A, 24B and 26, inner surface 312 of the centralbody 302 and surfaces 314-323 of the first and second legs 304, 306 arepreferably solid, while the outer surfaces 326 that contact bone whenimplanted are preferably porous. Further, prosthesis 300 preferablyincludes a solid rim 328 that runs along the outer boundaries of theprosthesis and connects the outer surfaces 326 with the inner surfaces312 and 314-323 of the prosthesis 300. The rim is preferably constructedfrom a solid material that spans the entire thickness of the prosthesisat the outer boundaries. Such boundaries may occur at intersectionsbetween bone contact surfaces and implant interfacing surfaces, that is,surfaces that directly contact or face the joint prosthesis or areconnected to the joint prosthesis via adhesive. Other boundaries inwhich the solid rim may be found occur at the interface 329 between thecentral body 302 and legs 304, 306. The rim at this interface 329 mayalso be formed of solid material, which extends through the entireprosthesis thickness to reduce the risk of fracture at that junction.The solid rim 328 provides strength and structural support to the porousstructure, particularly during impaction, and also helps tosignificantly reduce or eliminate potential sharp edges that can formwhere a hard porous structure comprises an outer boundary of an object.In some embodiments, the entire prosthesis 300 may be porous, or thelegs 304, 306 may be entirely porous and the central body 302 entirelysolid.

In some embodiments, the outer surface 326 of prosthesis 300 may alsohave discrete sections that are porous and discrete sections that aresolid. This may be particularly useful where a patient's bone structurehas significantly deteriorated to the point that the bone defects are nolonger contained within the cortical bone. In this scenario, prosthesis300 can take the place of the deteriorated cortical bone by providingdiscrete sections of the outer surface, or even entire legs, with solidmaterial to act as cortical bone.

The porous and solid portions of prosthesis 300 may be precisely formedby SLM as described in the heretofore referenced applicationsincorporated by reference herein, for example, and could even be formedas patient specific in instances where the bone defects are known priorto the surgical procedure. Additionally, prosthesis 300 may be formedand provided in various sizes in conformance with a database thatcatalogues the specific anatomy of a selected population of individuals.As previously mentioned, the methods of forming a bone void previouslydescribed herein may be utilized in implanting prosthesis 300. As such,a frustoconical reamer may form a central void for receipt of thecentral body 302 and may form two adjacent and offset frustoconicalvoids for receipt of the first and second legs 304, 306. In somescenarios, where a bone defect only exists lateral or medial of the IMaxis, a central void and only one offset void may be formed, and aprosthesis with a central body 302 and only one leg 304, 306 may beimplanted therein. Implantation is achieved by connecting an impactiontool to the impaction feature 324 and using a mallet, or some otherblunt instrument, to impact prosthesis 300 into the formed bone void.Generally impaction is ceased when surfaces 314, 316, 308 are coplanarwith resected surfaces 352, 354, 356 of the bone 354. The tapered natureof the frustoconical voids and frustoconical central body 302 and legs304, 306 provides a tight press fit such that all or most bone contactsurfaces 326 are firmly pressed against the bone 350, which facilitatesbony ingrowth into the porous structure.

Once prosthesis 300 is implanted, a joint prosthesis with a stemcomponent 360 may be implanted. The stem 360 is inserted through thecentral body 302 where the operator has the freedom to adjust the stem360 in multiple directions, particularly in an anterior-posteriordirection to precisely seat the joint prosthesis onto the bone 350. Bonecement, such as polymethyl methacrylate, may be placed between thecentral body inner surface 312 and stem 360 and also along surfaces314-323 to join the joint prosthesis with prosthesis 300 and bone 350.Stepped surfaces provided on surfaces 316, 318, and 323 and optionally314, 321, and 322 help prevent the separation of cement at theprosthesis-cement interface under loaded conditions. As such, thestepped surfaces are generally formed such that the stepped surfacestaper outwardly in the direction of the loads under normal operatingconditions.

FIG. 28A depicts another void filling prosthesis 400. Void fillingprosthesis 400 is frustoconical shaped and has an aperture 403 extendingthrough its entire length. Recesses 402 extend through the sidewall ofprosthesis 400 to provide free space in order to receive a keel of ajoint prosthesis, such as a tibial baseplate prosthesis. The outersurface 408 of the prosthesis is preferably constructed of a porousmaterial while the inner surface 404 is preferably solid. Additionally,the inner surface 404 may include a stepped surface to facilitate cementadhesion. The inner surface 404 generally tapers inwardly from theproximal end 410 to the distal end 412 and the stepped surfaces provideresistance to loads at the cement-prosthesis interface.

Similar to prosthesis 300, a solid rim 406 is provided around theboundary of prosthesis 400 to provide strength and reduce the likelihoodof sharp edges created by the porous structure, as best shown by FIG.28B. Additionally, the rim 406 at the proximal end of prosthesis 400 mayhave a groove or a channel to receive bone cement or other adhesive inorder to facilitate a firm connection between a joint prosthesis andprosthesis 400.

In an alternative embodiment, void filling prosthesis 400 may have asimilar construction to that of body 302 of void filling prosthesis 300such that the aperture 403 extends through the sidewall of prosthesis400 at an anterior or posterior location. Such embodiment of prosthesis400 may also have a curved portion with a similar frustoconical orcylindrical geometry, and a first and second wall portions that havesimilar planar or curved geometries. In such an embodiment, recesses 402may extend through the first and second sidewalls to create space forthe receipt of a tibial baseplate keel. This embodiment may be implantedinto a tibia bone, while the opening formed in the sidewall by theaperture would allow the operator flexibility in positioning the stem sothat a tibial baseplate connected thereto may be properly positioned onthe proximal tibial resection.

Prosthesis 500, as depicted in FIG. 29A, is similar to prosthesis 400,but differs in that prosthesis 500 includes a frustoconical lobe 504portion for receipt of a keel of a joint prosthesis. Prosthesis 400generally includes a body 502 and a lobe portion 504. The body 502generally has a frustoconical profile, and the lobe portion 504 isgenerally a bump-out of the sidewall of the body 502 in the shape of aconical frustrum. Additionally, this lobe portion 504 has a central axisthat is obliquely angled with respect to the central axis of the body502. However, in some embodiments, these axes may be parallel. Also, insome embodiments, prosthesis 400 may include two lobe portions that aresymmetrically arranged with body 504, which may be beneficial inaddressing lateral and medial bone deformities. In some embodiments, onelobe may have a central axis parallel with the central axis of the body502, and the other lobe portion may have a central axis obliquely angledwith respect to the body 502.

In further embodiments, the aperture extending through body 502 may alsoextend through the sidewall of the body 502 at an anterior or posteriorlocation much like that of body 302 of void filling prosthesis 300. Suchopening formed in the sidewall would still allow for the lobe portion504 and the recess 506 as the recess 506 and lobe portion 504 tend to belocated more laterally and medially. This opening would also form acurved portion and a first and second wall portions much like that ofbody 302. However, in such an embodiment, the lobe portion 504 may beformed out of the first or second wall portion. Thus, in one embodiment,the curved portion could be cylindrical or frustoconical, the first wallportion could be planar or curved and have recess 506 extendingtherethrough, and the second wall portion could form lobe 504. In somecircumstances where two lobe portions are desired, both the first andsecond wall portions can form the two lobe portions.

The lobe portion 504 may include an indented portion in its innersurface in order to accommodate large keels that extend into the innersurface of the lobe portion to prevent impingement of the prostheses. Insome embodiments, as depicted in FIG. 29B, this indent may be a void inthe inner surface of the lobe 504 such that the porous outer surface isexposed to the prosthesis aperture. This in and of itself may allowenough space for the prosthesis keel. However, where more space isdesired, a cutting tool, such as a modified hole punch, may be utilizedto remove the porous structure entirely from the void. Such features addto the universality of the prosthesis so as to reduce the number ofresecting instruments and void filling prostheses in the operating room.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims. Moreover, itwill also be appreciated that the features described in connection withindividual embodiments may be shared with others of the describedembodiments.

1. A method of replacing a distal femur, comprising: removing a firstfemoral prosthesis previously implanted on the distal femur; forming abone void at an end of the distal femur; inserting a void fillingprosthesis into the bone void such that a body of the void fillingprosthesis is positioned within the bone void and legs of the voidfilling prosthesis extending from the body are positioned entirelywithin the bone void; and implanting a second femoral prosthesis ontothe distal femur after inserting the void filling prosthesis into thebone void.
 2. The method of claim 1, wherein the forming step includesreaming the distal femur.
 3. The method of claim 1, wherein theinserting step includes impacting the void filling prosthesis into thebone void in a press-fit manner.
 4. The method of claim 1, wherein theimplanting step includes inserting an intramedullary stem of the secondfemoral prosthesis through an opening extending through the body.
 5. Themethod of claim 4, wherein the opening extends through a sidewall of thebody along an entire length of the body, and the inserting step includespositioning the opening in the sidewall of the body within the bone voidso that the opening faces an anterior direction.
 6. The method of claim5, wherein the inserting step is performed until an end surface of eachleg is flush with or positioned beneath a resected surface of the distalfemur.
 7. The method of claim 6, wherein the implanting step includespositioning a cam box of the second femoral prosthesis within a spacebetween the legs.
 8. The method of claim 7, wherein the implanting stepincludes placing bone cement between an inner surface of the voidfilling prosthesis and the second femoral prosthesis.
 9. A method ofreplacing a distal femur, comprising: forming a bone void at an end ofthe distal femur; inserting a void filling prosthesis into the bone voidsuch that a body of the void filling prosthesis is positioned within thebone void and legs of the void filling prosthesis extending from thebody are positioned within the bone void, the body having an openingextending through the body in a proximal-distal direction and through asidewall thereof in an anterior direction, the opening extending throughthe sidewall along an entire length of the sidewall; and implanting ajoint prosthesis onto the distal femur after inserting the void fillingprosthesis into the bone void.
 10. The method of claim 9, wherein theforming step includes reaming the distal femur with a reamer.
 11. Themethod of claim 9, wherein the forming step includes forming the bonevoid such that it tapers inwardly in a distal to proximal direction. 12.The method of claim 9, wherein the implanting step includes inserting anintramedullary stem of the joint prosthesis through the opening in thebody and positioning a femoral component of the joint prosthesis ontoresected surfaces of the distal femur.
 13. The method of claim 12,wherein each leg of the void filling prosthesis includes steppedsurfaces, and the implanting step includes placing bone cement betweenthe stepped surfaces and the femoral component.
 14. The method of claim9, wherein the inserting step is performed until an end surface of eachleg is flush with or positioned proximal to a distal most resectedsurface of the distal femur.
 15. The method of claim 9, wherein theimplanting stem includes placing bone cement between an inner surface ofthe void filling prosthesis and the joint prosthesis.
 16. A method ofreplacing a distal femur, comprising: forming a bone void at an end ofthe distal femur; inserting a void filling prosthesis into the bone voidsuch that a body of the void filling prosthesis is positioned within thebone void and legs of the void filling prosthesis extending from thebody are positioned within the bone void, the body having an openingextending through the body in a proximal-distal direction and through asidewall thereof in an anterior direction; and implanting a jointprosthesis onto the distal femur after inserting the void fillingprosthesis into the bone void.
 17. The method of claim 16, wherein theforming step includes reaming the distal femur with a reamer with aconical reamer such that at least a portion of the bone void has a shapecorresponding to the conical reamer.
 18. The method of claim 16, whereinthe opening in the body extends through the sidewall along its entirelength.
 19. The method of claim 16, wherein the implanting step includespositioning a cam box of the second femoral prosthesis within a spacebetween the legs.
 20. The method of claim 16, wherein the inserting stepincludes impacting the void filling prosthesis into the bone void in apress-fit manner so that the entire void filling prosthesis ispositioned within the bone void.